The present invention relates to a display controller.
Moving Picture Experts Group Phase 4 (MPEG-4) has been standardized as a coding method for multimedia information such as video data, still image data, and sound data (MPEG-4 Visual Part (ISO/IEC 14496-2: 1999 (E))). In recent years, a portable electronic instrument such as a portable telephone is provided with an encoding/decoding function compliant with the MPEG-4 standard. Such an encoding/decoding function enables a portable telephone to encode video data obtained by using a camera (CCD) and transmit the encoded data to another portable telephone (server), or to decode video data received from another portable telephone (server) through an antenna and display the decoded video data in a display (LCD) panel.
When performing multimedia processing such as MPEG-4 encoding/decoding processing, a series of processing may be entirely implemented by using a hardware processing circuit (ASIC) (first method).
However, since the scale of the hardware processing circuit is increased by using the first method, it is difficult to deal with a demand for a reduction in size of the portable electronic instrument and a reduction in power consumption.
A portable electronic instrument such as a portable telephone includes a host central processing unit (CPU) for controlling the entire instrument and realizing a baseband engine (communication processing). Therefore, multimedia processing such as MPEG-4 processing may be implemented by software processing using the host CPU (second method).
However, since the second method increases the processing load imposed on the host CPU, the time necessary for the host CPU to perform processing other than the multimedia processing is limited, whereby the performance of the electronic instrument including the host CPU is decreased. Moreover, since the processing time of the host CPU is increased, power consumption is increased, so that it is difficult to deal with a demand for a reduction in power consumption in order to increase the battery life.
As a third method, multimedia processing may be implemented by using a host CPU and a digital signal processor (DSP). Specifically, the entire multimedia processing program group for encoding and decoding video (MPEG) data, still image (JPEG) data, and sound (audio and voice) data is stored in a built-in memory (nonvolatile memory such as a flash ROM) of the DSP. The host CPU transmits a start command, and the DSP executes a multimedia processing program indicated by the start command.
However, the third method requires that the DSP execute a series of complicated multimedia processing. Therefore, as the number of types of codec is increased or the number of types of additional processing such as stream data multiplexing/separation is increased, the architecture of assigning the entire multimedia processing to the DSP becomes meaningless, so that the performance of the DSP and the system is decreased. Moreover, since the clock frequency of the DSP must be increased in order to deal with the multimedia processing which has become complicated, problems such as an increase in power consumption and generation of heat occur. Furthermore, since the third method requires that the entire multimedia processing program group be stored in the built-in memory (flash ROM) of the DSP, power consumption and product cost are increased due to an increase in the capacity of the memory.